This invention relates to a two-component developer containing a toner and a carrier. More particularly, the toner comprises quaternary ammonium salt and/or a nitrogen-containing polymer as a positive charge-controlling agent and the carrier is coated with polyolefinic resin.
A two-component developing method, in which insulating nonmagnetic toner particles are mixed with carrier particles to be frictionally charged and these particles are carried and brought into contact with electrostatic latent images to develop electrostatic latent images, has been known as an electrostatic latent image-developing method.
The carrier particles used in such the two-component developing method have been usually coated with suitable materials on account of reasons such as the prevention of toners from forming films on surfaces of carrier particles, the formation of a surface having uniform properties, the prevention of surface oxidation, the prevention of deterioration resistance to humidity, the prolongation of useful life time of developers, the protection of a photosensitive member from damages or abrasion by carriers, the control of chargeable polarity and the control of a charging quantity.
Polyolefinic resins have been known as such a coating material.
As the chargeability of toner is usually much influenced by the combination of toner with carrier, the coating material should be selected in its individual combination.
Japanese Patent Laid-Open No. Hei 2-22673 discloses a developer for developing electrostatic latent images containing a carrier coated with a fluorine resin. The carrier of the present invention is coated with a polyolefinic resin different from the fluorine resin. There is neither disclosed nor suggested anywhere that the toner used in the combination with the carrier coated with fluorine resin may be used in the combination with the carrier coated with polyolefinic resin as disclosed in the present invention. Accordingly, a carrier coated with a polyolefinic resin should be studied individually in relationship to a toner used therewith in response to the properties of the carrier.
A toner, one of elements of the two-component developer, usually contains a charge controlling agent on account of adjustment of charging level and security of charging stability. A positive-charge controlling agent is added to a positively chargeable toner.
However, as a polyolefinic resin itself tends to be charged negatively, some positive-charge controlling agents work to charge a toner positively to excess. When the usage of such the positive-charge controlling agents is decreased to lower the charging level, the uniform dispersion of the positive-charge controlling agent into toner becomes difficult and so the charging stability can not be secured and toner particles come to scatter.